In addition, it is used only in a batch system and is difficult to couple with flow injection (FI). A drawback of this method is that the presence of oxidizing substances in the sample precludes the reduction of Hg 2+ to Hg 0 by ultrasound (Gil et al. Reduction of Hg 2+ to Hg 0 was accomplished in a sonoreactor owing to the reducing gases and radicals formed upon sonolysis of formic acid added to the sample solution. 2007), which also eliminates the need for conventional reducing agents. Sono-induced vapor generation technique has also been reported as a green vapor generation method (Gil et al. This process obviates the need for expensive and high-purity reducing reagents (i.e., NaBH 4 or SnCl 2), is amenable to speciation analysis with or without chromatographic separation, and is less prone to interference from concomitant ions. Hydrogen and carboxyl radicals that arise from photodissociation of low molecular weight organic acids (e.g., formic, acetic, and propionic) are employed to reduce metal or nonmetal ions to the volatile vapor. 2011) utilizes a photoreaction process based on UV-vis irradiation. Furthermore, adsorption of gaseous reaction products reduces vapor generation efficiency. Transition metal ions interfere with the vapor production by being reduced and deposited on the cathode surface. Second, the cathode surface requires frequent conditioning, typically on a daily basis. First, the cathode material must be carefully selected because it strongly influences the performance of the electrochemical process. However, there are several shortcomings for EcHG (Denkhaus et al. The most significant advantage of electrochemical generation is that it obviates the need for chemical reducing reagents. 2007), which uses electrons as reductants, has been shown to be a suitable alternative to chemical HG. Electrochemical vapor generation (EcHG) (Denkhaus et al. In addition, traditional tetrahydroborate (III)-based chemical HG methods are prone to interferences by transition metals due to their interaction with the reducing reagent or catalytic decomposition of the reaction products on the surfaces of the reduced concomitant metals (He et al. However, these reducing agents are expensive and unstable (i.e., freshly prepared reagents are required). This HG reaction is very efficient and can be accomplished in both batch and online systems. For example, sodium tetrahydroborate (III) was commonly used in HG for reduction. 2012), including hydride generation (HG), elemental vapor generation, alkylation, halide generation, and metal-carbonyl generation, usually make use of chemical reducing agents for vapor generation. Several chemical vapor generation techniques have been developed, including conventional chemical vapor generation, electrochemical hydride generation, photochemical vapor generation (photo-CVG), sono-induced vapor generation, thermo-chemical vapor generation, and plasma-induced vapor generation (plasma-CVG).Ĭonventional chemical vapor generation technologies (Smichowski and Farías 2000, D’Ulivo 2004, D’Ulivo et al. Metal or nonmetal ions in liquid sample can be converted into volatile species by various chemical vapor generation techniques, which not only greatly increase the sample introduction efficiency but also reduce the matrix interference effectively. We also discuss the possible mechanism and future trends in plasma-CVG in this review.Ĭhemical vapor generation is an effective sample-introduction technique (Wu et al.
This review summarizes the developments of plasma-CVG, including solution cathode glow discharge plasma and dielectric barrier discharge plasma, for several analytes determination. Its analytical applications have been demonstrated in analysis of Hg, Cd, Se, Zn, As, Sb, Te, Os, and I. Comparing with conventional vapor generation method, plasma-CVG offers several other advantages: sensitive and simple in operation, high vapor generation efficiency, and rapid reaction kinetic speed. The most distinguished characteristic of plasma-CVG is that it avoids the use of chemical reduction/oxidation reagents. Plasma-induced vapor generation (plasma-CVG), where the dissolved ions are converted to volatile species by the plasma-induced chemical process, is an emerging green vapor generation technique. Chemical vapor generation is widely used as an efficient sample-introduction technique for atomic spectrometry.